Steel cords for reinforcing rubber articles such as pneumatic tires have a variety of twisting structures. In order to achieve so-called rubber penetration (easiness of penetration of rubber between filaments during rubber coating), usually, the form of filaments is enlarged thereby providing adequate interstices between filaments, or sheath filaments are arranged around core filaments in a number slightly smaller than the maximum allowable number thereby providing adequate interstices.
Specifically, for example, Patent Document 1 discloses a steel cord including core filaments composed of a plurality of core wires aligned on the same level, and a plurality of side wires twisted around the core filaments so as to form a flat cross section, wherein interstices are provided between the core and side wires at the ends of the steel cord in the width direction.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-180387